1. Field of the Invention
The present invention relates to a method for forming a pattern onto an article during an injection molding thereof and an apparatus for the same, for preventing impressions of a heating board from remaining on the surface of the molded article or molding.
2. Description of the Related Art
Conventionally, as decorative patterning methods for three-dimensional solid moldings, a laminate method and a transfer printing method are known. In the laminate method, after a film on which a pattern has been printed is shaped or concurrently therewith, the film is adhered to a substrate, or while or after the film is shaped, the film is filled with a resin. On the other hand, in the transfer printing method, only a pattern ink of a film on which the pattern has been printed is transferred to a molded article or molding.
As a transfer printing method, a method disclosed in Japanese Patent Laid-Open Publication Serial No. SHO 62-196113, published on Aug. 29, 1987 is known. In this method, as will be described later, a heating board which absorbs a pattern-bearing film thereon is moved into a space between a male mold and a female mold which are spaced apart from each other by a predetermined distance. Then the pattern-bearing film heated by the heating board is vacuum absorbed to the inner surface of the female mold. Thereafter, the heating board is retreated to the outside of the space between the male mold and the female mold. Next, the male mold and the female mold are clamped or closed. In the cavity defined by these molds, a molten resin is injected to form a molded article. Thus, the pattern-bearing film is attached to the surface of the molded resin article.
However, in this method, when the pattern-bearing film is absorbed to the heating board, air is caught between the heating board and the pattern-bearing film. This air remains as air bubbles. Thus, the pattern-bearing film is not uniformly heated. In addition, marks or impressions of vacuum holes defined on the heating board remain on the surface of the final molding having the pattern-bearing film absorbed thereby. Thus, the appearance of the molding is adversely affected.
To solve this problem, a method as disclosed in Japanese Patent Laid-Open Publication Serial No. HEI 3-96320 has been proposed. In this method, a pattern-bearing film absorbing surface of a heating board is formed of an uneven surface having a large number of concave and convex portions. With these concave and convex portions, a large number of passageways are formed so as to allow the air to escape. In this method, although air bubbles may be prevented, if the pattern-bearing film is thin, the impressions of the concave and convex portions and the vacuum holes remain on the pattern-bearing film. Thus, the appearance of the molding is deteriorated.